In U.S. Pat. No. 5,614,683 to Kranbuehl, which is herein incorporated by reference, it was demonstrated that average molecular weight was an important indicator of the life expectancy of a Nylon 11 (polyamide formed from 11-aminoundecanoic acid). In particular, the patent demonstrated that average molecular weight measurements correlated with elongation measurements for the aged polyamide, and that one could use the molecular weight measurement to identify when polyamide parts needed to be replaced.
Life monitoring of plastic and composite parts continues to grow in importance in modern industrial processes. As plastic materials replace metal materials in load bearing applications as well as in extreme and corrosive environments, there is a continuing need for improved methods to ascertain when a part should be replaced. Replacing after a pre-set period of time runs the dual risks of (1) waiting too long replace the part—i.e., in some situations the aging may occur earlier than the pre-set period, and (2) replacing the part too early—i.e., the part could have considerable life left even after the pre-set period expires.